As one of IP mobility technologies heretofore known, a mobile internet protocol version 6 (mobile IPv6) technology is disclosed in Non-patent Document 1 described below. The mobile IPv6 technology is a technology capable of receiving a packet to be sent to an MN even in a case where the MN changes an access router (hereinafter sometimes referred to as the AR) which is a connected destination to an IP network.
The mobile IPv6 technology includes the following procedure by which the MN can receive an IP packet to be sent to a home address (hereinafter sometimes referred to as the HoA) assigned to the MN at a new connected destination to the IP network.
When the MN changes the AR to be connected and acquires a new IP address (hereinafter sometimes referred to as a care-of address or a CoA), the MN notifies a home agent (hereinafter sometimes referred to as the HA) of a home network connected to the IP network of the CoA. The IP packet transmitted to the HoA from a correspondent node (hereinafter sometimes referred to as the CN) which is a communication partner (a communication partner device) of the MN is sent to the home network via the IP network. However, the HA is notified that the MN acquires the CoA. Therefore, this IP packet to be sent to the CoA is subjected to packet tunneling (see Non-patent Document 2 described below), and a routing header (see Non-patent Document 3 described below) in which the HoA is described is added before transmitting the packet. This IP packet transmitted to the CoA reaches the MN via the IP network, and the MN processes the routing header added to the IP packet to recognize that this IP packet is addressed to itself (the HoA).
Moreover, according to the mobile IPv6 technology, by the following procedure, the MN can transmit the IP packet to the CN from the new connected destination to the IP network.
To transmit the IP packet to the CN, the MN cannot set the HoA as a source of the IP packet. This is because a router of the IP network does not transfer the IP packet transmitted from a network-topologically contradictory address, and discards the packet based on a security problem (see Non-patent Document 4 described below). Therefore, the MN subjects the IP packet to be sent to the CN to the packet tunneling in order to send the packet to the HA, and adds a home address option in which the HoA is described to transmit the packet. This IP packet transmitted from the MN to the HA is sent to the HA via the IP network. The HA processes the home address option added to the IP packet to recognize that the IP packet is a packet transmitted from the MN. After subjecting the packet to packet detunneling (see Non-patent Document 3), the packet is sent to the home network. This IP packet transmitted from the HA to the CN is sent to the CN via the IP network.
Moreover, according to the mobile IPv6 technology, by the following procedure, the MN can receive the IP packet from the CN via the new connected destination to the IP network without passing through the HA. It is to be noted that this function is referred to as route optimization. The above technique concerned with the transmission of the IP packet via the HA is possible even in a case where the CN does not correspond to the route optimizing function. However, the technique concerned with the transmission of the IP packet without passing through the HA as described below is possible in an only case where the CN corresponds to the route optimizing function.
On changing the AR to be connected and acquiring the CoA, the MN notifies the HA of the CoA and also notifies the CN of the CoA. When the CN corresponds to the route optimization, the CN returns a response message to this notice. In the following description, it is assumed that the CN corresponds to the route optimization. To transmit the IP packet to the MN, the CN adds the routing header in which the HoA is described to a transmission packet, and transmits the IP packet to the CoA. This IP packet transmitted from the CN to the CoA is sent to the MN via the IP network. The MN processes the routing header added to the IP packet to recognize that this IP packet is to be sent to itself (the HoA).
Furthermore, according to the mobile IPv6 technology, by the following procedure, the MN can transmit the packet to be sent to the CN corresponding to the route optimization from the new connected destination to the IP network without passing through the HA.
As described above, to transmit the IP packet to the CN, the MN cannot set the HoA as the source of the IP packet. Therefore, the MN sets the CoA as a source address, and adds the home address option in which the HoA is described before transmitting the packet. This IP packet transmitted from the MN to the CN is sent to the CN via the IP network. The CN corresponding to the route optimization processes the home address option added to the IP packet to recognize that this IP packet is a packet transmitted from the MN.
On the other hand, as one of problems of the mobile IPv6 technology, in a case where the MN has a state in which a certain CoA (hereinafter referred to as the old CoA here) is acquired, and changes from a state in which the MN is connected to a certain AR (referred to as the old AR here) to a state in which the MN is disconnected from the old AR and is connected to another new AR to acquire a new CoA, there is a problem that, in some case, the IP packet transferred or transmitted from the HA or the CN to the old CoA before the disconnection from the old AR does not reach the MN connected to the new AR, before the HA or the CN is notified of the new CoA.
As one of techniques for solving this problem, a fast handover technology is disclosed in Non-patent Document 5 described below. According to the fast handover technology, the packet tunneling from the old AR (the previous access router: PAR) to a new access router (NAR) to be connected is performed to transfer, to the NAR, the packet which has reached the old CoA, before the HA or the CN is notified of the new CoA. In consequence, the MN can receive, from the NAR, the packet which has reached the old CoA.
In addition, as development of a multicast technology of transmitting the IP packets to a plurality of nodes, a technology referred to as eXplicit multicast (Xcast, see Non-patent Document 6 described below) exists. According to this Xcast technology, a plurality of destination addresses are set to the IP packet, a reception node which first receives this IP packet transfers the IP packet to another node that has not received the packet, and the transfer is successively repeated to distribute the IP packets to all of the plurality of destination addresses. Alternatively, the router which transfers this IP packet analyzes the plurality of destination addresses. In a case where the next hop (the next transfer destination) concerned with the plurality of destination addresses differs, the distribution of the IP packet is branched. In consequence, the IP packet can be multicast to all of the plurality of destination addresses. Moreover, fusion of the Xcast technology and the existing network constitution is also investigated by use of a hop-by-hop option which can be interpreted by the only router having a specific function. Furthermore, there is also a technology in which the IP packet is multicast through both base stations connected to the MN before and after the handover by use of this Xcast technology to realize smooth connection switching during the handover (see Non-patent Document 7 described below).    Non-patent Document 1: D. Johnson, C. Perkins, J. Arkko, “Mobility Support in IPv6”, draft-ietf-mobileip-ipv6-24, Dec. 29, 2003, Work In Progress, <http://www.ietf.org/internet-drafts/draft-ietf-mobileip-ipv6-24.txt>.    Non-patent Document 2: Conta, A. and S. Deering, “Generic Packet Tunneling in IPv6 Specification”, RFC2473, December 1998, <http://www.ietf.org/rfc/rfc2473.txt>.    Non-patent Document 3: Deering, S. and R. Hinden, “Internet Protocol, Version 6 (IPv6) Specification”, RFC 2460, December 1998, <http://www.ietf.org/rfc/rfc2460.txt>.    Non-patent Document 4: Ferguson, P. and D. Senie, “Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing”, RFC 2267, January 1998, <http://www.ietf.org/rfc/rfc2267.txt>.    Non-patent Document 5: K. Rajeev, “Fast Handovers for Mobile IPv6”, draft-ietf-mipshop-fast-mipv6-01, Jan. 30, 2004, Work In Progress, <http://www.ietf.org/internet-drafts/draft-ietf-mipshop-fast-mipv6-01.txt>.    Non-patent Document 6: R. Boivie, N. Feldman, Y. I mai, W. Livens, D. Ooms, O. Paridaens, “Expilicit Multicast (Xcast) Basic Specification”, draft-ooms-xcast-basic-spec-05, August 2003, Work In Progress.    Non-patent Document 7: Y. Ezaki, Y. Imai, “Mobile IPv6 handoff by Explicit Multicast”, draft-ezaki-handoff-xcast-01, May 2001, Work In Progress.
However, the above-mentioned conventional IP mobility technology has the following problems.
(A) It is possible to set only one of an IP address expected to be used by a receiver and an IP address of the AR expected to be connected to the receiver in one of a sender of the IP packet and a gateway (GW) which is present between the sender and the receiver. As a result, in a case where the IP address set by the sender is not used by the receiver currently or the receiver is not connected to the AR set by the sender, a problem occurs that the IP packet is discarded.
(B) Especially, in a case where the receiver moves at a high speed, there is a problem that the receiver causes delay in notifying the sender of information on the movement and that the problem of the above (A) remarkably appears.
(C) In the fast handover technology described in Non-patent Document 5, the packet tunneling technology between the ARs is used. In a case where the receiver moves at a high speed and moves over many ARs, a problem of scalability is generated.
(D) In the Xcast technology described in Non-patent Document 6, since all of the destination addresses described in the IP packet need to be successively visited, there is a problem that much time is required until the final node is reached. When a trouble is generated in an intermediate node or the intermediate node moves and the packet cannot therefore reach the packet, there is a problem that any packet is not distributed to the subsequent node. Since the IP packet is distributed to all of the plurality of destination addresses set to the IP packet, the IP packet is branched into packets as many as the plurality of set destination addresses, and traffic might increase. These problems especially remarkably appear, as the number of the destination addresses set to the IP packet increases. Furthermore, to realize smooth communication during the handover by use of the Xcast technology described in Non-patent Document 7, the IP packet received by the MN might become redundant or lost before and after the handover, and there is a problem that efficient communication cannot necessarily be realized.